Services run by Arriva Trains Wales, CrossCountry and First Great Western all suffered delays of up to two hours due to damage to cables near the Dyffryn Estate, Newport.

Buses replaced trains for a period between Cardiff Central and Newport as rail operators worked to fix damage to line-side signalling equipment.

The problems began just after midday today after Network Rail reported a loss of power to signals between Newport and Marshfield.

Officers from British Transport Police and Network Rail engineers discovered three 650V power cables had been cut.

Power was restored to the signalling system after workers were able to “splice together” the cut cables and the rail lines were fully reopened at 2.25pm.

Network Rail initially believed the problems were caused by an attempted cable theft, but later said the incident was being treated as vandalism.

Many passengers across the South Wales rail network experienced delays to their journeys as a result of the cable vandalism.

Crowds of passengers filled the lobby of Cardiff Central station as they awaited information on their train services.

Cardiff University student Nicholas Clifton was waiting on a service to Chippenham, Wiltshire, to take part in a gig with his soul band.

The 22-year-old, who is studying a PHD in neuroscience, said: “The last time I was here there was a landslide, which stopped me getting to where I wanted to, so it seems like there’s always some disruption.”

Spike Jones, 40, of Fairwater, Cardiff, who was travelling to Salisbury to visit a friend, said he was not too badly affected by the disruption on the line.

He said: “I travel on the trains a lot and there seem to be a huge amount of delays, most recently because of the flooding in Devon and Dorset, which had a knock-on effect.”

Beth MacDonald was eagerly checking her phone for updates on her rail service to London Gatwick.

The 18-year-old University of Glamorgan student, from Sussex, said: “Everyone is trying to get home for Christmas, so there are a lot more suitcases.”

An Arriva Trains Wales spokesman said: “All trains between Cardiff Central and Newport were stopped between 12pm and 2pm as Network Rail and British Transport Police investigated the incident which occurred between the two stations and completed repairs. Delays continued into the afternoon as services returned to normal.

“We would like to thank those passengers affected for their patience whilst we worked hard to resolve this difficult situation. We would also like to remind passengers to use www.journeycheck.com/arrivatrainswales before travelling to find the best information relating to disruption.”

A British Transport Police (BTP) spokesman said: “BTP officers were called to the railway line near Dyffryn Estate, Newport, after Network Rail reported a loss of power to signals in the area.

“The incident was reported to BTP at 12.02pm.

“Officers attended along with engineers from Network Rail and discovered damage had been caused to lineside signalling equipment.

“The incident led to a number of trains being delayed or cancelled, causing disruption for passengers and the rail industry. The lines were fully reopened at 2.25pm.

“Enquiries are ongoing to trace those responsible for the damage.”

Anyone with information on the damage can contact British Transport Police on 0800 40 50 40, or Crimestoppers anonymously on 0800 555 111. In all calls, please quote incident reference 250 of 14/12/2012.